Hollow article made of thermoplastic resin, manufacturing method of the hollow article, and manufacturing apparatus of the hollow article

ABSTRACT

A hollow article is manufactured to have a configuration in which the wall thickness of each of both end portions changes multidirectionally with extremely high accuracy. A device for first pushing a thermoplastic resin into a cavity ( 9 ) of a neck mold ( 6 ) in contact with an annular orifice nozzle ( 30 ) for plastic, and then manufacturing a tubular parison  18   a  having various different cross sections throughout the whole length with moving the neck mold apart from the annular orifice nozzle, a controller for a drive unit for moving the neck mold onto/apart, provided so as to be operable while the neck mold ( 6 ) is moving apart from the annular orifice nozzle ( 30 ), and a controller for a drive unit for changing an outlet gap ( 3 ) of the annular orifice nozzle, and means for increasing the speed from zero while the neck mold is moving apart from the annular orifice nozzle, are provided, a nozzle mouthpiece constituting the annular orifice nozzle ( 30 ) is multi-divided vertically and laterally, the divided part is disposed so as to be able to reciprocate laterally, a part ( 2   a ) of the upper portion of the nozzle mouthpiece is replaced with a blow mold  11,  and further a part lower than it holds the filling-up thermoplastic resin upon blowing and is released when a product is taken out.

BACKGROUND OF THE INVENTION

[0001] (i) Field of the Invention

[0002] The present invention relates to a hollow article made of athermoplastic resin and having both end portions whose wall thicknesschanges multidirectionally with extremely high accuracy, such astri-port type CV-joint boots for automobiles.

[0003] (ii) Description of the Related Art

[0004] Conventionally, as illustrated in FIG. 7 for example, a hollowarticle 8 such as a CV-joint boot for an automobile is known. In theCV-joint boot 8, one end portion (the upper end portion in FIG. 7) 40has been formed by injection molding and all other portions have beenformed by blow molding. As an apparatus for manufacturing such a hollowarticle 8, an apparatus illustrated in FIG. 6 is known (Japanese PatentNo. 2556647).

[0005] The apparatus illustrated in FIG. 6 is a parison manufacturingapparatus for blow-molding bellows (hollow article) 8, in which thebellows is blow-molded with its cross-sectional profile being changedinto a wave shape through the whole length of a parison 18, asillustrated in FIG. 6. Since the circular parison 18 is never flatlycompressed, the plastic is extended evenly throughout the wholeperiphery. This prior art is very superior for molding such bellows 8.In the bellows molded with this apparatus, since its one end portion(the upper end portion in FIG. 6) 40 is injection-molded with a neckmold, the thickness of that portion can be changed multidirectionally onthe circumference with high accuracy. In the portion other than the oneend portion 40, however, its thickness cannot but be uniform throughoutthe circumference because it is blow-molded. As a result, the apparatuscan provide only such a general automobile CV-joint boot (bellows) 8 asillustrated in FIG. 7. This point is a problem of the prior art, whichthe present invention is to solve in particular. More specifically, sometri-port type CV-joint boots, for example, may require not only a highdimensional accuracy at the one end portion 40 (the wall thickness mustbe changed multidirectionally with high accuracy) but also a highdimensional accuracy at the other end portion (the lower end portion inFIG. 6) 41 (the inner circumference must be formed unevenly in heightand the outer circumference must be formed into an accurate circle),that is, they may require an accurate shape at either of both endportions of the bellows, whose wall thickness is changedmultidirectionally. The above-described prior art, however, has aproblem that it can not meet this requirement. Further, in case of aconventional automobile CV-joint boot (FIG. 7) made with a manufacturingapparatus of this kind, the molded portion from the distal end of anozzle mouthpiece 2 to the other end 41 of the CV-joint boot is anunnecessary portion, and such an unnecessary portion is very large. Thisbrings about a problem that a great deal of waste is generated. On theother hand, Japanese Patent Application Laid-open No. 10-272679discloses a method in which, upon injection-blow molding, the mold forthe final product shape portion (portion corresponding to the other endportion 41 in the above-described prior art) is not changed forinjection molding and for blow molding and it is successively molded,and thereby no flash is generated and the dimensional accuracy is kept.By this technique, only the other end portion as the final product shapeportion 41 meets the above-described object, but the one end portion(portion corresponding to the one end portion 40 in the above-describedprior art) is blow-molded by changing an injection mold and a blow moldwith each other. Therefore, even by this technique, a configuration inwhich the wall thickness at both ends is changed multidirectionally withhigh accuracy can not be formed. So, as a result of repeating earneststudies and examinations, by improving the manufacturing apparatus ofthe above-described prior art (Japanese Patent No. 2556647), the presentapplicant has succeeded in newly developing a hollow article made of athermoplastic resin and having both end portions whose wall thicknesschanges multidirectionally with extremely high accuracy, a manufacturingmethod of the hollow article, and a manufacturing apparatus for thehollow article.

SUMMARY OF THE INVENTION

[0006] The present invention has been developed in view of such problemsof the prior art, and its object is to provide a hollow article made ofa thermoplastic resin and having both end portions whose wall thicknesschanges multidirectionally with extremely high accuracy.

[0007] Technical measures made by the present invention to solve theabove problems are as follows. A hollow article made of a thermoplasticresin is formed by bringing a cavity of a drawing unit into contact withan outlet gap of an annular orifice nozzle made up of a nozzle coreconstituted so as to be upwardly and downwardly movable, and a nozzlemouthpiece concentrically surrounding said core to form said outlet gaphaving a variable gap width for upward extruding the thermoplastic resinbetween it and said core; injecting the thermoplastic resin into saidcavity through said outlet gap to form one end portion having aconfiguration in which a wall thickness changes multidirectionally withextremely high accuracy; drawing and forming a tubular parison whilemoving said drawing unit apart from said annular orifice; blow-moldingthe tubular parison after replacing an uppermost portion of said nozzlemouthpiece constituting said outlet gap with a blow mold to form ahollow article body; injection-molding the other end portion of a hollowarticle having a configuration in which a wall thickness changesmultidirectionally with extremely high accuracy, through a cavity havinga desired shape of said nozzle mouthpiece at a lower portion; andlaterally moving said blow mold and said nozzle mouthpiece upon takingout a product to open them. A typical example of the hollow article is atri-port type CV-joint boot for an automobile.

[0008] A manufacturing apparatus for the hollow article is as follows.

[0009] The apparatus comprises an annular orifice nozzle made up of anozzle core constituted so as to be upwardly and downwardly movable, anda nozzle mouthpiece concentrically surrounding said core to form anoutlet gap having a variable gap width for upward extruding athermoplastic resin between it and said core; a drawing unit having acavity of a desired shape downward opened for forming one end portion ofa hollow article, said drawing unit being moved apart from said annularorifice nozzle to draw and form a tubular parison after injecting thethermoplastic resin into said cavity on said outlet gap of said annularorifice nozzle; and a blow mold for blow-molding said tubular parison toform a hollow article body of a desired shape, wherein said nozzlemouthpiece is multi-divided vertically and laterally, each divided partis disposed so as to be able to reciprocate laterally, an uppermostportion of said nozzle mouthpiece divided is constituted so as to bereplaceable with said blow mold upon blow molding, and a lower portionof said nozzle mouthpiece has a desired cavity and said blow mold andsaid nozzle mouthpiece can be moved laterally upon taking out a productafter forming the other end portion of the hollow article into a desiredshape to open them. The above nozzle mouthpiece is divided into at leasta portion for forming the outlet gap, and a portion forinjection-molding the other end portion of the hollow article having aconfiguration in which a wall thickness changes multidirectionally withextremely high accuracy.

[0010] The nozzle mouthpiece multi-divided vertically and laterally canhave an individual independent temperature conditioning system to setthe thermoplastic resin in the nozzle mouthpiece at a proper temperatureany time.

[0011] A manufacturing method of the above hollow article comprises thesteps of bringing a cavity of a drawing unit into contact with an outletgap of an annular orifice nozzle made up of a nozzle core constituted soas to be upwardly and downwardly movable, and a nozzle mouthpiececoncentrically surrounding said core to form said outlet gap having avariable gap width for upward extruding a thermoplastic resin between itand said core; injecting the thermoplastic resin into said cavitythrough said outlet gap to form one end portion having a configurationin which a wall thickness changes multidirectionally with extremely highaccuracy; drawing and forming a tubular parison while moving saiddrawing unit apart from said annular orifice; blow-molding the tubularparison after replacing an uppermost portion of said nozzle mouthpiececonstituting said outlet gap with a blow mold to form a hollow articlebody; injection-molding the other end portion of a hollow article havinga configuration in which a wall thickness changes multidirectionallywith extremely high accuracy, with a cavity having a desired shape at alower portion of said nozzle mouthpiece; and then laterally moving saidblow mold and said nozzle mouthpiece upon taking out a product to openthem, thereby forming a hollow article having both end portions whosewall thickness changes multidirectionally with extremely high accuracy.

[0012] In the present invention, the shape of the one end portion isdetermined by the cavity shape of the neck mold. On the other hand, theshape of the other end portion is determined by that the cavity (spaceshape) defined by the nozzle mouthpiece of the annular orifice nozzleand the outer side surface of the nozzle core serves as a flow passagefor the thermoplastic resin when pushing into the neck mold and whenextruding the parison, and keeps the thermoplastic resin filling up thelower portion of the space shape upon blow molding. At this time, thethermoplastic resin filling up the upper portion of the annular orificenozzle is expanded to the inner wall surface of the blow mold bycompressed gas blown into the parison after part of the upper portion ofthe nozzle mouthpiece is replaced with the blow mold while keeping thenozzle core intact, and the shapes of the parison and the other endbecome one continuous body. This makes it possible to manufacture such ahollow article made of a thermoplastic resin and having both endportions whose wall thickness changes multidirectionally with extremelyhigh accuracy. Further, in case of, e.g., an automobile CV-joint bootmade with this manufacturing apparatus, in which the outer diameter ofthe other end is larger than that of the one end, the unnecessary moldedportion from the distal end of the nozzle mouthpiece to the other endportion of the CV-joint boot becomes small and there is an advantagethat the amount of waste generated becomes very little. Here, the nozzlemouthpiece multi-divided vertically and laterally can have an individualindependent temperature conditioning system, and it can be adjusted andset at temperatures at which the thermoplastic resin in the nozzlemouthpiece is made easy to flow upon flowing, easy to blow upon blowing,and solidified at a short time.

[0013] The present invention provides not only the manufacturingapparatus of the hollow article but also a method for molding a specifichollow article by manufacturing a specific parison and a specific shapeusing a specific apparatus. In this respect, the present invention canalso make it possible to, for example, first push a thermoplastic resininto a cavity of a neck mold in contact with an annular orifice nozzlefor plastic, then form a parison with moving said neck mold apart fromsaid annular orifice nozzle, said parison being a tubular parison havingvarious different cross-sections throughout the whole length of theparison so that the wall thickness of the parison formed may change intoa wave shape through troughs and peaks, operate a controller for a driveunit for moving the neck mold onto/apart and a controller for a driveunit for changing plastic flowing out through an outlet gap of saidannular orifice nozzle, while moving the neck mold apart from saidannular orifice nozzle, said outlet gap of said annular orifice nozzlebeing changed in accordance with the quantity of the plastic flowingout, increase the speed of said neck mold from zero when moving the neckmold apart from said annular orifice nozzle, and operate bothcontrollers as described above to work in the period when said neck moldis further moving apart. Here, the characteristic features of thepresent invention are in that the nozzle mouthpiece constituting theannular orifice nozzle is multi-divided vertically and laterally, eachdivided portion is disposed so as to be able to reciprocate laterally,part of the upper portion of the nozzle mouthpiece is replaced with theblow mold, and further, part lower than that keeps the thermoplasticresin filling up also upon blowing and is made to be able to open andclose for taking out a product, and thereby, a hollow article is formedhaving both end portions whose wall thickness changes multidirectionallywith extremely high accuracy.

[0014] A hollow article of the present invention can be constructed inconsideration of various use objects. Besides, the manufacturing methodand the manufacturing apparatus for the hollow article of the presentinvention are particularly advantageous because they are constructed sothat they can manufacture tri-port type CV-joint boots. Such a boot isprovided for use on the transmission side of an automobile, and itrequires not only a high accuracy in dimension of one end portion butalso, in the other end portion, an accurate configuration in which thewall thickness changes multidirectionally, i.e., the profile of theouter periphery must be made into an accurate circle while protrusionsare formed on the inner peripheral side. Important points when using itare not only the point that the bellows manufactured according to thepresent invention is made of a thermoplastic elastomer, but also in thathigh accurate bellows both end portions can be obtained because it canbe manufactured with more accuracy by setting the neck mold, the annularorifice nozzle, and the divided nozzle mouthpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a sectional view of a manufacturing apparatus for ahollow article made of a thermoplastic resin according to an embodimentof the present invention;

[0016]FIG. 2 is a block diagram illustrating the construction of acontroller of the hollow article manufacturing apparatus illustrated inFIG. 1;

[0017]FIG. 3 is a schematic view of a stroke measuring device of thehollow article manufacturing apparatus illustrated in FIG. 1;

[0018]FIG. 4 is a sectional view of bellows (tri-port type CV-jointboot) manufactured with the manufacturing apparatus for the hollowarticle illustrated in FIG. 1;

[0019]FIG. 5 is an example of operation conceptional views when a hollowarticle is manufactured with the manufacturing apparatus for the hollowarticle illustrated in FIG. 1, in which (a) illustrates a state that aneck mold sits on an annular orifice nozzle, (b) illustrates a statethat the neck mold rises from the annular orifice nozzle to startforming a parison, (c) illustrates a state that the neck mold completesthe rising operation and the parison has been formed, (d) illustrates astate that a nozzle mouthpiece is divided after forming the parison, (e)illustrates a state that the nozzle mold has been replaced with a blowmolding split mold, (f) illustrates a state that the replaced blowmolding split mold is closed, (g) illustrates a state that the parisonis being blow-molded into the final shape in the blow molding splitmold, and (h) illustrates a state that, after completion of blowmolding, the blow molding split mold and the nozzle mouthpiece aredivided and a product having been blow-molded into the final shape istaken out;

[0020]FIG. 6 is a sectional view of a prior art for blow-moldingbellows; and

[0021]FIG. 7 is a sectional view of bellows manufactured with theparison manufacturing apparatus illustrated in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will bedescribed with reference to drawings. Note that this embodiment isnothing but an embodiment used for only describing the present inventionin detail and the present invention should not be interpreted limitedlyto this embodiment. FIG. 1 is a vertical sectional view illustrating anembodiment of a manufacturing apparatus for a hollow article made of athermoplastic resin according to the present invention, FIG. 2 is ablock diagram illustrating the construction of a controller of themanufacturing apparatus for the hollow article, FIG. 3 is a conceptionalview of a stroke measuring device, FIG. 4 illustrates an embodiment ofthe hollow article made of the thermoplastic resin, in which (a) is avertical sectional view and (b) is a bottom view, and FIG. 5 is aschematic view illustrating steps of a manufacturing method for thehollow article according to the present invention.

[0023] A hollow article of the present invention comprises both endportions 40 and 41 each having a constitution in which the wallthickness of these end portions formed by injection molding athermoplastic resin changes multidirectionally with extremely highaccuracy, and a hollow article body (bellows) 8 integrally formed byblow molding between both end portions 40 and 41. A typical examplethereof is a tri-port type CV-joint boot for an automobile illustratedin, e.g., FIG. 4 by way of example. Both end portions of the blow-moldedbellows as the hollow article body 8, i.e., one end portion 40 as theupper end portion in FIG. 1 and the other end portion 41 as the lowerend portion, are each constructed so as to have a configuration in whichthe wall thickness changes multidirectionally with extremely highaccuracy (see FIG. 4(a) and (b)). For example, in this embodimentillustrated in FIG. 4, the one end portion 40 is formed so that theinner diameter 40 a is made into a substantially accurate circle and theouter diameter 40 b is made uneven in height on the periphery. On theother hand, the other end portion 41 is formed so that the outerdiameter 41 a is made into a substantially accurate circle and the innerdiameter 41 b is made uneven in height on the periphery. Either of bothend portions 40 and 41 thus has a configuration in which the wallthickness changes multidirectionally. Although this uneven shape is notparticularly limited, since both end portions 40 and 41 are formed byinjection molding, a multidirectional change in wall thickness can beobtained with extremely high accuracy. The shape of this hollow articlebody 8 should not be interpreted limitedly to the illustrated shape.Besides, also either shape of both end portions 40 and 41, i.e., theconfiguration in which the wall thickness changes multidirectionally,should not be interpreted limitedly to the illustrated shape. They canbe changed in design within the scope of the present invention. Thethermoplastic resin as the material of the hollow article should notparticularly be limitedly interpreted, and the optimum material canproperly be selected within the scope of the present invention. Besides,although, in this embodiment, a tri-port type CV-joint boot for anautomobile is described as an embodiment of the hollow article, thisonly shows one optimum embodiment. The hollow article of the presentinvention should not at all be interpreted limitedly to this, and anyother form can properly be selected within the scope of the presentinvention. That is, it is needless to say that, if both end portions ofa hollow article body to be blow-molded are formed by injection moldingso that the wall thickness may change multidirectionally, the presentinvention is applicable to a product in a field not having any relationto the joint boot of this embodiment.

[0024] An embodiment of a hollow article manufacturing apparatus formanufacturing this hollow article will be described next. Amanufacturing apparatus for a tri-port type CV-joint boot (hollowarticle) for an automobile illustrated in, e.g., FIG. 1 is mentioned asa typical example. Generally dividing the hollow article manufacturingapparatus illustrated in FIG. 1, it is made up of an annular orificenozzle 30, a drawing unit 6, and a blow mold 11. The manufacturingapparatus of the present invention is constructed so that a nozzlemouthpiece of the annular orifice nozzle 30 is multi-divided and thedivided nozzle mouthpiece can reciprocate laterally, and part of thenozzle mouthpiece is replaceable with the blow mold 11. It has acharacteristic feature in a relation between such a construction and thedrawing unit 6.

[0025] The annular orifice nozzle 30 is made up of a nozzle core 1constituted so as to upwardly and downwardly move, and nozzlemouthpieces 2 a, 2 b, and 2 c concentrically surrounding the nozzle core1. The nozzle core 1 and the nozzle mouthpiece 2 a define an outlet gap3 in the form of an annular orifice at the upper portion. Athermoplastic resin 4 is supplied to the outlet gap 3 through an annularchamber between the nozzle core 1 and the nozzle mouthpiece 2 a. Asdescribed above, the nozzle mouthpiece is made up of three parts, i.e.,the nozzle mouthpieces 2 a, 2 b, and 2 c (three-divided construction).The nozzle mouthpieces 2 a and 2 b are vertically fixed and eachlaterally two-divided so as to be able to open and close. Note that, inthis embodiment, although the nozzle mouthpiece is verticallythree-divided and laterally two-divided, this is nothing but only oneembodiment, and the vertical and lateral division construction isoptional. The nozzle mouthpiece 2 b has a cavity 17 on the innercircumference for injection-molding the other end portion (the lower endportion in FIG. 1) of the hollow article with the outer circumference ofthe nozzle core 1. The nozzle core 1 has a size/shape so as to form adesired flow passage between it and the nozzle mouthpieces 2 a, 2 b, and2 c. On the outer circumferential surface opposite to the cavity 17 ofthe nozzle mouthpiece 2 b, it has a shape corresponding to the innerdiameter 41 a of the other end portion 41 of the hollow article to beinjection-molded, and it is constructed so as to be upwardly anddownwardly movable in an axial direction (vertically in FIG. 1) inaccordance with an arrow 5 in FIG. 1. The construction of the flowpassage is not particularly limited and it can be changed in designwithin the scope of the present invention at need. In this embodiment,since the other end portion 41 of the hollow article is injection-moldedso as to have a configuration in which the wall thickness changes sothat the outer diameter 41 b is made into an accurate circle and theinner diameter 41 a is uneven in height, the inner surface shape of thecavity 17 is made into a shape corresponding to that and the outercircumferential shape of the nozzle core 1 is made into a shapecorresponding to the uneven shape of the inner diameter 41 a. Note that,if any one or either of the inner and outer diameters 41 a and 41 b ofthe other end portion 41 of the hollow article has a shape which can beinjection-molded so as to have a construction in which the wallthickness changes multidirectionally, the inner surface shape of thecavity 17 and the outer circumferential shape of the nozzle core 1should not particularly be limitedly interpreted and they can properlybe changed in design within the scope of the present invention. Thenozzle mouthpieces 2 a and 2 b are opened and closed by horizontallyreciprocating as shown by arrows 12 b and 12 c in FIG. 1. In contrastwith this, the nozzle core 1 disposed in the interior can be upwardlyand downwardly moved in accordance with the arrow 5 in FIG. 1, asdescribed above. That is, by the up/down operation of the nozzle core 1,the width of the outlet gap 3 formed between it and the mouthpiece 2 ais controlled to be wide and narrow. By this width control of the outletgap 3, the parison 18 a formed with moving the drawing unit 6 apart fromthe annular orifice nozzle 30 can be formed into a tubular shape havingvarious different cross sections throughout the whole length (forexample, the thickness of the parison wall changes into a wave shapethrough troughs 36 and peaks 37). Note that the shape of the parison 18a should not particularly be limitedly interpreted and one not havingvarious different cross sections throughout the whole length like thisembodiment is also within the scope of the present invention. Althoughan up/down mechanism for the nozzle core 1 is disclosed in FIG. 1, theconstruction of this embodiment is nothing but one embodiment and itshould not be interpreted limitedly to this, and for example, a drivingunit, a stroke measuring device, and a controller constituting theup/down mechanism are also not limited, and another optimum constructioncan be adopted within the scope of the present invention.

[0026] Here, each of the nozzle mouthpieces 2 a, 2 b, and 2 cmulti-divided vertically and laterally has an individual independenttemperature conditioning system, and it can be adjusted and set attemperatures at which the thermoplastic resin in the nozzle mouthpieceis made easy to flow upon flowing, easy to blow upon blowing, andsolidified at a short time. As this temperature conditioning system, awell-known construction can properly be selected within the scope of thepresent invention, and can be changed in accordance with thethermoplastic resin used. Besides, the nozzle mouthpieces 2 a, 2 b, and2 c can have heat-insulating structures at the respective contactsurfaces, which is within the scope of the present invention. Besides,these heat-insulating structures may also be well-known structures.

[0027] The drawing unit 6 is disposed above the annular orifice nozzle30 to be opposite to the nozzle 30. The drawing unit (hereinafter alsoreferred to as neck mold (injection die)) 6 is constituted so as to beupwardly and downwardly movable in accordance with an arrow 7 in FIG. 1,and it is for injection-molding one end portion (the upper end portionin FIG. 1) 40 of the hollow article and forming a cylindrical parison 18a by drawing up. The neck mold 6 surrounds the front end portion of ablow mandrel 10, and it defines a cavity open downward, in cooperationwith the outer circumference of the blow mandrel 10. The open side ofthe cavity 9 communicates with the outlet gap 3 when the neck mold 6sits on the annular orifice nozzle 30. The cavity 9 is forinjection-molding the one end portion (the upper end portion in FIG. 1)40 of the hollow article and formed into a shape so that the wallthickness of the one end portion 40 changes multidirectionally withextremely high accuracy. This cavity 9 should not particularly belimitedly interpreted, and it can properly be changed in design withinthe scope of the present invention. Although an up/down mechanism forthe drawing unit 6 is disclosed in FIG. 1, the construction of thisembodiment is nothing but one embodiment and it should not beinterpreted limitedly to this, and for example, a driving unit, a strokemeasuring device, and a controller constituting the up/down mechanismare also not limited, and another optimum construction can be adoptedwithin the scope of the present invention.

[0028] As for the blow mold, FIG. 1 only illustrates a blow moldingsplit mold 11 as one part of the blow mold, but both blow molding splitmolds 11 are horizontally reciprocated as shown by an arrow 12 a to openand close (see FIG. 5(e) to (h)). The blow molding molds define inside apredetermined cavity 13. Although the profile of the cavity 13 shouldnot particularly be interpreted limitedly to the illustrated form, it isformed so as to correspond the hollow article body 8 to be formed byblow molding. For example, in this embodiment, the profile of the cavity13 must correspond to the outer profile of the hollow article body(bellows) 8 when the blow mold is closed, as illustrated in FIG. 6. Notethat the height of the inner surface shape of each blow molding splitmold 11 is the sum of the height of the inner surface shape of thenozzle mouthpiece 2 a and the height of the parison 18 a.

[0029] The nozzle mouthpieces 2 b and 2 c have slanting surfaces 22 aand 22 b in their upper portions. When both blow molding split molds 11are closed, the blow molding split molds 11 are put on the slantingsurface 22 a with a supporting surface 23 a slanting correspondingly.The supporting surface 23 a is provided on the lower surface of anannexed portion 25 a. Similarly, when the divided nozzle mouthpiece 2 bis closed, the divided nozzle mouthpiece 2 b is put on the slantingsurface 22 b with a supporting surface 23 b slanting correspondingly.The supporting surface 23 b is provided on the lower surface of anannexed portion 25 b. The annexed portions 25 a of both blow moldingsplit molds 11 and the annexed portion 25 b of the divided nozzlemouthpiece 2 b are advanced toward the slanting surfaces 22 a and 22 bupon closing, respectively. Although the illustration is omitted, eachblow molding split mold 11 and the nozzle mouthpiece 2 a can slide alonghorizontal rails attached on a rack. The rack supports a blow moldoperation device made up of two double-acting piston-cylinder units anda nozzle mouthpiece 2 a operation device. Each of the double-actingpiston-cylinder unit engages with one blow molding split mold 11 and onenozzle mouthpiece 2 a. In addition, this rack itself engages with thedouble-acting piston-cylinder units and slides along horizontal rails sothat each blow molding split mold 11 and the nozzle mouthpiece 2 a maybe replaceable. Further, pressure liquid is supplied through a conduitto any of the double-acting piston-cylinder units. By a similar method,the nozzle mouthpiece 2 b also can reciprocate.

[0030] Referring to FIG. 1, a platform 43 supports a neck mold drivingdevice 46. The driving device 46 engages with an annexed portion 45 ofthe neck mold 6 for moving the neck mold 6. Like the blow molding moldoperation device and the nozzle mouthpiece operation device as describedabove, the driving device 46 is also constructed as a piston-cylinderunit. Pressure liquid is supplied to the piston-cylinder unit through aconduit 42. On the other hand, the platform 43 also supports a nozzlecore driving device 47. The driving device 47 comprises apiston-cylinder unit and engages with the nozzle core 1. Also to thepiston-cylinder unit supplied is pressure liquid through the conduit 42.As described above, the driving devices 46 and 47 are nothing but oneembodiment and they are not limitative. In FIG. 1, reference numeral 44denotes a pressurizing piston. With the pressurizing piston 44, adriving device 48 constructed as a piston-cylinder unit engages. It isused for forcibly sending the thermoplastic resin toward the outlet gap3. Also, these pressurizing piston 44 and driving device 48 are nothingbut one embodiment and they are not limitative. The above conduits 42are open to oil pressure control valves 50, 51, and 52, respectively.With the oil pressure control valves 50, 51, and 52, not only the flowof the pressure liquid can be stopped, but also the flow rate of thepressure liquid flowing in a unit time can be adjusted or controlled.Each of the oil pressure control valves 50, 51, and 52 is connected witha main conduit 54. The pressure liquid is supplied to the manufacturingapparatus through the main conduit 54. Stroke measuring devices 14, 15,and 16 are disposed for the neck mold 6, the nozzle core 1, and thepressurizing piston 44, respectively. The stroke measuring devices 14,15, and 16 are only schematically illustrated in FIG. 1. As illustratedin FIG. 2, these stroke measuring devices 14, 15, and 16 send outmeasurement data to a computer 21. A program set based on specificbellows to be manufactured or a parison to be manufactured accordinglyis supplied to the computer from a memory 24. The computer 21 controlsthe oil pressure control valves 50, 51, and 52 in accordance with theprogram and the measurement data sent out from the stroke measuringdevices. FIG. 3 schematically illustrates a stroke measuring device tobe used in three ways, which is constructed as a supersonic strokereceiver. The supersonic stroke receiver includes a movable ring magnet26 using a permanent magnet. The ring magnet 26 is connected with amovable member, and the movement distance or position of the movablemember is measured relatively to the zero point position. The ringmagnet 26 is provided with a measuring tube 29. The measuring tube 29 ismade of a ferromagnetic material and disposed at a fixed position. Themeasuring tube 29 is stopped at its one end with a sound-absorbingmaterial 31 and a measuring wire 32 is incorporated therein. To theother end portion of the measuring wire 32, an electric pulse issupplied from an electric pulse transmitter 33. The electric pulse runsalong the measuring wire 32 with generating a circular magnetic filed,till the magnetic field reaches the ring magnet 26 and the ring magnet26 sends out an acoustic pulse. The acoustic pulse is received by thesupersonic pulse receiver 34. The time lag between the pulsetransmission and the pulse reception is a scale for the current positionof the movable member, i.e., the ring magnet 26. Also the strokemeasuring devices 14, 15, and 16 and controller are nothing but oneembodiment and they are not limitative, as described above.

[0031] Next, an embodiment of a manufacturing method will be describedwith reference to FIG. 5(a) to (h). In this embodiment, a hollow articleis formed through the steps in the order of(a)→(b)→(c)→(d)→(e)→(f)→(g)→(h) illustrated in FIG. 5. The neck mold 6is first in a state of being moved down for time being, it sits on thecentral region of the nozzle core 1 with an end portion of the blowmandrel 10, and a thermoplastic resin 4 is injected into the cavity 9 toinject-mold one end portion (also referred to as plastic neck portion)40 (FIG. 5(a)). The one end portion 40 is formed so as to have aconfiguration in which the wall thickness changes multidirectionallywith extremely high accuracy, because it is formed by injection molding.When the neck mold 6 is moved upward with further extruding thethermoplastic resin through the outlet gap 3, a cylindrical parison 18 ais drawn and formed (FIG. 5(b) and (c)). This parison manufacture startpoint 19 is the time point when the neck mold 6 sits downward on theannular orifice nozzle 30 (as illustrated in FIG. 1). The parisonmanufacture end point 20 is the time point when the neck mold 6 occupiesthe upper limit position illustrated in FIG. 1 (a state of FIG. 1 andFIG. 5(d)). Besides, at this time, the nozzle core 5 can axiallyreciprocate as shown by the arrow 5. It advances upon the completion ofthe parison manufacture to come into contact with the most front edge ofthe nozzle mouthpiece 2 c, where a product portion and a molten resinportion are separated. Since the other end portion 41 isinjection-molded in the cavity 17 of the nozzle mouthpiece 2 b, theother end portion 41 is formed so as to have a configuration in whichthe wall thickness changes multidirectionally with extremely highaccuracy. Next, both nozzle mouthpieces 2 a are moved in, e.g., X-Ydirections so that they may not interfere with both blow molding splitmolds 11 (FIG. 5(d)). After this, both blow molding split molds 11 aremoved to close (FIG. 5(e) and (f)). Compressed gas is supplied throughthe blow mandrel 10, and the parison 18 a and the parison 18 b areblow-molded into the final shape within the blow molding split molds 11to form a hollow article body 8 and become a continuous one body withthe other end portion 41 (FIG. 5(g)). Since the cylindrical parisons 18a and 18 b are never flatly compressed, the plastic is extended evenlythroughout the whole periphery. As a result, the generated waste portionbecomes less than in case of an extrusion-blow molding. The nozzlemouthpiece 2 b is moved to open at the same time when both blow moldingsplit molds 11 are moved to open, and the product in the upper portionthan the front end of the nozzle mouthpiece 2 c is drawn up by the neckmold 6 (FIG. 5(h)). The parison 18 has, e.g., six wall section thickportions 35 distributed over the whole length. Each wall section thickportion 35 extends from one trough 36 through one peak 37 to the nexttrough 36 and it gives the wall cross section a wave shape as a whole.As illustrated in FIG. 4, the hollow article body (bellows) 8manufactured from the parison 18 a has specific crest portions 38separated by specific isthmus portions 39. Therefore, the hollow articlebody (bellows) 8 has at its both ends one end portion 40 and the otherend portion 41 each having a configuration in which the wall thicknesschanges multidirectionally with extremely high accuracy.

[0032] Since the present invention is constructed as described above, itcan provide a hollow article having a configuration in which the wallthickness of each of both end portions changes multidirectionally withextremely high accuracy, and an apparatus and method for manufacturingthe hollow article. Therefore, the provision of a hollow article havingboth ends whose wall thickness changes multidirectionally with highaccuracy, e.g., a tri-port type CV-joint boot for an automobile, whichthe prior art (e.g., Japanese Patent No. 2556647 and so on) never couldachieve, can be intended accurately and surely. Besides, according tothe manufacturing method and apparatus of the present invention, theunnecessary molded portion from the distal end of the nozzle mouthpieceto the other end portion of the CV-joint boot becomes little, and thereis an advantage that the amount of waste generated becomes very little.Besides, since the nozzle mouthpiece multi-divided vertically andlaterally is provided with an individual independent temperatureconditioning system, it can be adjusted and set at temperatures at whicha thermoplastic resin in the nozzle mouthpiece is made easy to flow uponflowing, easy to blow upon blowing, and solidified at a short time.

What is claimed is:
 1. A hollow article made of a thermoplastic resinwhich is formed by: bringing a cavity of a drawing unit into contactwith an outlet gap of an annular orifice nozzle made up of a nozzle coreconstituted so as to be upwardly and downwardly movable, and a nozzlemouthpiece concentrically surrounding said core to form said outlet gaphaving a variable gap width for upward extruding the thermoplastic resinbetween it and said core; injecting the thermoplastic resin into saidcavity through said outlet gap to form one end portion having aconfiguration in which a wall thickness changes multidirectionally withextremely high accuracy; drawing and forming a tubular parison whilemoving said drawing unit apart from said annular orifice; blow-moldingthe tubular parison after replacing an uppermost portion of said nozzlemouthpiece constituting said outlet gap with a blow mold to form ahollow article body; injection-molding the other end portion of a hollowarticle having a configuration in which a wall thickness changesmultidirectionally with extremely high accuracy, through a cavity havinga desired shape of said nozzle mouthpiece at a lower portion; andlaterally moving said blow mold and said nozzle mouthpiece upon takingout a product to open them.
 2. The hollow article having both endportions of a configuration in which a wall thickness changesmultidirectionally with extremely high accuracy according to claim 1,wherein the hollow article is a tri-port type CV-joint boot for anautomobile.
 3. A manufacturing method of a hollow article comprising thesteps of: bringing a cavity of a drawing unit into contact with anoutlet gap of an annular orifice nozzle made up of a nozzle coreconstituted so as to be upwardly and downwardly movable, and a nozzlemouthpiece concentrically surrounding said core to form said outlet gaphaving a variable gap width for upward extruding a thermoplastic resinbetween it and said core; injecting the thermoplastic resin into saidcavity through said outlet gap to form one end portion having aconfiguration in which a wall thickness changes multidirectionally withextremely high accuracy; drawing and forming a tubular parison whilemoving said drawing unit apart from said annular orifice; blow-moldingthe tubular parison after replacing an uppermost portion of said nozzlemouthpiece constituting said outlet gap with a blow mold to form ahollow article body; injection-molding the other end portion of a hollowarticle having a configuration in which a wall thickness changesmultidirectionally with extremely high accuracy, with a cavity having adesired shape at a lower portion of said nozzle mouthpiece; and thenlaterally moving said blow mold and said nozzle mouthpiece upon takingout a product to open them, thereby forming a hollow article having bothend portions whose wall thickness changes multidirectionally withextremely high accuracy.
 4. A manufacturing apparatus of a hollowarticle comprising: an annular orifice nozzle made up of a nozzle coreconstituted so as to be upwardly and downwardly movable, and a nozzlemouthpiece concentrically surrounding said core to form an outlet gaphaving a variable gap width for upward extruding a thermoplastic resinbetween it and said core; a drawing unit having a cavity of a desiredshape downward opened for forming one end portion of a hollow article,said drawing unit being moved apart from said annular orifice nozzle todraw and form a tubular parison after injecting the thermoplastic resininto said cavity on said outlet gap of said annular orifice nozzle; anda blow mold for blow-molding said tubular parison to form a hollowarticle body of a desired shape, wherein said nozzle mouthpiece ismulti-divided vertically and laterally, each divided part is disposed soas to be able to reciprocate laterally, an uppermost portion of saidnozzle mouthpiece divided is constituted so as to be replaceable withsaid blow mold upon blow molding, and a lower portion of said nozzlemouthpiece has a desired cavity and can be moved laterally upon takingout a product after forming the other end portion of the hollow articleinto a desired shape to open them.
 5. The manufacturing apparatus of thehollow article according to claim 4, wherein said nozzle mouthpiece isdivided into at least a portion for forming the outlet gap, and aportion for injection-molding the other end portion of the hollowarticle having a configuration in which a wall thickness changesmultidirectionally with extremely high accuracy.
 6. The manufacturingapparatus of the hollow article according to claim 4 or 5, wherein saidnozzle mouthpiece multi-divided vertically and laterally can have anindividual independent temperature conditioning system to set thethermoplastic resin in the nozzle mouthpiece at a proper temperature anytime.